Suicide's undiminished impact on a family informs Egan's poignant first novel, the tale of an 18-year-old retracing her older sister's doomed excursion through Europe. As a child, Phoebe O'Connor felt less vital than her sister Faith. Their father, a frustrated artist, lived vicariously through the aptly named elder girl; Faith learned to please him by taking extravagant physical risks, and after his death, her apparent free-spiritedness masked the same desperate need to impress her peers. (The ``Invisible Circus,'' one character explains, was a late-'60s ``be-in'' that ``was all about watching ourselves happen,'' and Faith embraced this celebration of spontaneity.) But Faith lost faith-in 1968 when, on a trip with her boyfriend, she mysteriously fell from a cliff in Italy. Ten years later, Phoebe crosses the Atlantic, her itinerary mapped by Faith's falsely optimistic postcards, to learn how and why Faith died. The younger sister at first fails to realize that her impossibly romantic image of her sibling has left her suspended in time. She's leading only an artificial life dictated by a ghost, and Egan effectively contrasts Phoebe's rigidity with Faith's daring nature. Eventually, however, she discovers that Faith ``just threw herself away.'' Though the prose at times overexaggerates in conveying such extreme personalities, the author usually manages to keep it in check as Phoebe chooses her own future over Faith's forsaken one. (Jan.)